1. FIELD OF THE INVENTION
The present invention relates to passive sway arrest systems for cargo container transporting cranes, and more particularly, to an integrated passive sway arrest system for dockside cargo container handling cranes having a trolley which moves a suspended cargo container lifting spreader fore and aft on a girder and extended boom and which utilizes the wire rope and the sheave system which supports the load beneath the trolley to arrest sway in the suspended moving load.
2. DESCRIPTION OF THE PRIOR ART
Prior to the present invention, many systems have been devised and utilized for the purpose of arresting load sway for cargo container handling cranes. Some of those are disclosed in patents owned by the assignee of the present invention. They include U.S. patent application Ser. Nos.: 3,375,938; 3,532,324; 3,739,922; 3,825,128; 3,945,503; and 3,945,504.
One problem With some of these designs is that the wire ropes act like a spring when there is an appreciable length of rope reeved out and supporting the load, and a means of solving this problem was to install an energy absorber, such as a hydraulic cylinder, at the ends of the ropes in the reeving system to stop the spring action.
Sway arrest systems are of essentially two types: active and passive. An active system usually is defined as requiring some affirmative action to be taken to counteract the induced sway. To take such action, the sway must be sensed by some means whereby an appropriate selected counterforce can be actuated and applied. A passive sway arrest system can be in either an operative or inactive condition, but the passive system does not need to sense the sway: the system just needs to inherently react to sway when the system is in the operative condition.
A problem in arresting sway of a load is in being able to detect the sway at the ends of long suspension ropes if the need is to apply counteracting forces. However, a fairly unique system was developed for the purpose of attempting to detect sway and to arrest it, but it was unsuccessful. This prior art method was to suspend the wire rope reeving which supports the load from a sheave support platform which is pivoted to allow the platform to oscillate in partial rotation as the load swayed. Any rotational movement of the platform on its pivot axis could be sensed to determine when arresting forces should be applied. However, this did not work because when arresting forces were applied to straight hanging wire rope to dampen the oscillation of the platform, the load simply swung with the ropes remaining in a parallelogram. Thus, the system did not identify sway as an isolated movement because the load could swing independently of the rotatable platform, and the system was not able to arrest the sway that it did detect.
The arrangement of a partially rotatable sheave support platform does provide a means by which accurate sway detection can be accomplished when it is modified to allow loads to be applied to the suspension ropes of the sway arrest system which do counteract the sway, and the present invention accomplishes this result. However, the modifications of the prior art by the present invention create a very effective passive sway arrest system in addition to allowing accurate sensing of sway.